they are actually a crayfish but ive seen them called "freshwater lobsters" as well
he most likely would catch some of your smaller fish and eat them
some people clip of the "thumb" part of the pinchers to prevent that but i think thats pretty cruel
and i'm to squeemish anyway...and it does grow back so you would have to keep doing it...yuck
i think you tank is a little overcrowded but if the fish are doing well and your keeping the water params where they should be, i wouldnt worry about it too much...just means a little extra work for you
...be sure to keep testing your water as the fish get larger (if they arent full grown already)...bigger fish=more waste so you might have to adjust your maintance schedule as your fish grow
i would add some more live plants tho...even if they are just floating ones to help keep the water clean along with your water changes...certainly cant hurt
as far as the bala in there...i'd lose him unless your going to get him a larger tank and some friends...i think they get around 12" and need to be in a school
also tetras, khuliis and giant danios like to school so you might want to do some trading off to make some schools in there...blueberry tetras are dyed and will eventually lose theyre color anyway...its a cruel pratice that produces unhealthy fish alot of the time so i wouldnt get anymore of them, but you could get some white shirt tetras to go with him, cuz thats what he'll evetually be once his body processes the toxins...just my opinion
--liz